Giant tortoise longevity is no accident

There may never have been a sadder face in the animal world than that of the famous Galapagos tortoise, Lonesome George.

I was lucky enough in 2006 to have observed ‘the rarest creature in the world’ at close quarters in his special enclosure at the Charles Darwin Research Station (CDRS) on Santa Cruz Island.

After a long wait in hot sun, George was kind enough to amble slowly from the shade of a tree, raise his wrinkled neck and provide the denture-less smile you see in the accompanying picture.

Was there a twinkle in those dark brown eyes? Never one to be rushed, and by then believed to have been in his early 80s, George was working up to mating again.

Various females

Being the only known surviving Pinta Island tortoise (discovered there in 1971), CDRS staff had introduced various females of ‘compatible’ species to his enclosure on Santa Cruz over many years. But none caught George’s eye.

A reward of US$10,000 was posted for anyone who could provide a successful mate, but it went unclaimed. A couple of years after my visit, however, (no credit claimed), he mated with two penned females.

Sadly, none of the eggs was fertile, and when George died in June 2012, that was the end of the Punta Island tortoise. As to his actual age, there is considerable debate: the CDRS thinks he was born around 1910, which would have put him at 102, but Sir David Attenborough reckons George was only in his eighties.

Other species of Galapagos tortoise commonly live beyond 100 years, and the oldest has been recorded at a creditable 152.

In a related development, research published this month (December) by Nature Ecology and Evolution suggests Lonesome George and giant tortoises of other species may have had souped-up immune systems, top-shelf DNA repair and increased resistance to cancer.

The researchers have sequenced George’s genome and that of a giant tortoise from a different species that inhabits the Aldabra Atoll in the Indian Ocean.

Mammals harbour one copy of a gene that enables immune cells to punch holes in invading or abnormal cells; the two giant tortoises carried 12.

Genome-mending

George and his giant counterpart also sported a version of a DNA-fixing enzyme that may be more efficient, one of the signs that they are particularly good at mending genome damage.

Duplications of two genes that may quell tumour growth, along with other genomic differences from mammals, suggest the tortoises may have evolved stronger defences against cancer, which older animals are susceptible to.